In the past, servers transferring electronic messages accepted it from any sending server which was essential as the network connections were unreliable. If a given Sending server could not connect with the server of the recipient, it could at least pass over the message to any other relay server located closer to the recipient. This system however proven to be vulnerable to abuses from entities sending out unsolicited messages (SPAM) such as Unsolicited Commercial E-mail (UCE) or Unsolicited Bulk E-mail (UBE), which are illegal in many countries.
Reception of SPAM messages is presently out of control of the recipient, which at best (e.g. using appropriate filtering software) bears the costs of SPAM delivery, especially while accessing the net via dial-up connection. Transmission of SPAM also consumes resources of mail servers intermediating in this process. Mail servers receiving e-mails from any mail sending servers are called “open relay” servers and commonly such servers are not handled by other servers, because with a high′ probability it may be assumed that the e-mails sent by such servers are SPAM messages. When open relay server attempts to send a message, a recipient's server is able to determine its address and check whether this server is listed on the public list of “open relay” servers. Such lists are managed for example by the “MAPS” Organization (http://www.mail-abuse.com), which also administers lists of RBL servers (Realtime Blackhole List—list of servers spreading SPAM messages) and DUL servers (Dial-Up User List—list of servers connected via switched lines, from which servers SPAM messages are sent directly to recipient's servers).
Commonly used technique for protection against SPAM messages involves appropriate configuration of sending server in such a way that sender has to be authorized before sending a mail. Thanks to this solution, only mails from senders that may log on to the mail sending server and whose identity is in this way confirmed by this server, shall be transferred further to the addresses of receiving servers designated in the messages. In case of an electronic mail, such type of service is called as SMTP AUTH and is defined in RFC 2554 (Request For Comment) normalization standard.
Additional method used in connection with the one described above is a method in which receiving server accepts only e-mails for which the address of the sender corresponds to the address of the sending server. In other words, a sender is able to send messages only by means of the server being capable to authorize sender's identity. In practice, a sender authorization server is a server of a sender mail box or any other server connected with such a server, and a comparison of the sender address with the address of the sending server may consist in checking whether a domain part of sender FQDA address corresponds to a domain part of the sending server address.
Particular steps of a typical, prior art method of transferring e-mail messages between sender's mail user agent and recipient's mail user agent, employing both techniques described above are illustrated below with reference to FIGS. 1 and 4. FIG. 1 schematically illustrates typical system of transferring e-mails between sender's local computer system 1 and recipient's local computer system 4 by means of or through sender's mail server 2 and recipient's mail server 3, while FIG. 4—individual steps of transferring the message. Usually, particular computer systems 1-4 are located remotely to each other and interconnected by means of a network employing TCP/IP protocol. A local sender's mail user agent 11 is installed on the senders computer system 1 (such as sender's personal computer, laptop, etc.), while a local recipient's mail user agent 41 is installed on the recipient's computer system 14.
As shown in FIG. 4a, in the first step an e-mail message is created by the sender with usage of mail user agent 11. Except for its subject matter, an e-mail includes also among other things a FQDA address of at least one recipient and a FQDA address of the sender. Subsequently, local mail user agent 11 makes an attempt to login to a sender's server 2, on which the sender has its e-mail account. The login process is realized with using a SMTP AUTH mechanism as well as user name and passwords provided by the sender, which data are usually stored in encoded form by a local MUA 11 of the sender. If login process is performed correctly, sender's MUA 11 sends created e-mail message to a sender's server 2 and, if there is no more messages to send, interrupts connection with sender's server.
In the next step, which is not shown in FIG. 4, the sender's server 2 translates FQDA addresses of each of the recipients indicated in the message, and using DNS mechanism determines recipient's server 3 of each specified recipient. As shown in FIG. 4b, sending server 2 connects then with a server of a given recipient 3. At the present step of sending a message, each server making a connection with recipient's server 3 shall be rather recognized as “sending server” instead of “sender's server”, as its identity has not be yet verified. After establishing a connection, the sending server 2 indicates the sender of the message (using for example “MAIL FROM” command). If a domain part of a FQDA address does not match a domain part of the address of the sending server 2, a recipient's server 3 returns error reply informing about an error and refuses to accept the message. In the opposite instance, a recipient's server 3 returns OK reply enabling the sending server 2 to inform (for example using “RCPT TO” command) about the data of the recipient of the message, and, if a given receiving server 3 is suitable for the given recipient, to send messages and to disconnect.
An exemplary session of connection between the sending server 2 and the recipient's server 3 shown in FIG. 4b is presented below, where “R” denotes commands and replies send by the recipient's server and “S” denotes commands send by the sending server:
StepServerCommand(1)R:220BBN-UNIX.ARPA Simple MailTransfer Service Ready(2)S:HELO HOST1.USC-ISIF.ARPA(3)R:250 BBN-UNIX.ARPA(4)S:MAIL FROM:<Smith@USC-ISIF.ARPA>(5)R:250 OK(6)S:RCPT TP:<Jones@BBN-UNIX.ARPA>(7)R:250 OK(8)S:DATA(9)R:354 Start mail input; end with <CRLF>.<CRLF>(10) S:This is a test mail . . .S:Blah blah blah . . .S:.(11) R:250 OK(12) S:QUIT(13) R:221 BBN-UNIX.ARPA Service closingtransmissions channel
As shown, the sending server identified itself in step (2), and its domain part (USC-ISIF.ARPA) corresponds to domain part of the sender's address which was provided in step (4). It is of course one of the simplest systems of verification of the sender's server, as well as the sender itself. In the prior art methods of transferring of electronic message, data identifying the sender and/or recipient and/or the address of the sending server is contained most often in the message itself or follows from the actual IP address of the sending server or hitherto existing former history of transmission of the message.
The last step of a process of sending a message is its delivering to s a recipient's local mail user agent 41, residing in recipient's local computer system 4. As shown in FIG. 4c, a recipient's local mail user agents logs in to a recipient's server 3 and, after passing through a logging procedure, the MUA downloads e-mail messages stored on the recipient's server. The above discussed steps of a process of transferring electronic messages, as illustrated on FIGS. 4a and 4b, are carried out with using SMTP protocol, whereas during the steps illustrated on FIG. 4c POP3 or IMAP protocols are used.
European patent specification EP 1 575 228 discloses a method and apparatus for reducing e-mail spam and virus distribution in a communications network by authenticating the origin of e-mail messages. The described method includes receiving at the sender's server a query to determine whether an e-mail message was sent be an indicated (in this message) user; checking logged data at the sender's server to determine whether the e-mail message in fact corresponds to a message sent from the sender's server, and responding to said query to authenticate the e-mail message origin.
The term “known method” or “known method of transferring the message” as used in this specification, denotes a process of sending messages according to any known and used prior art method, and particularly according to the method illustrated by FIGS. 1 and 4.
Using known methods of sending electronic messages, message needs to be transferred three times: firstly between sender's local mail user agent 11 residing on sender's personal computer 1 and sender's mail server 2; secondly between sending mail server 2 and recipient's mail server 3: and for the third time between a recipient's server 3 and a recipient's local mail user agent 41. On the other side, common e-mail messages still grows larger in terms of a size of data that needs to be sent, what results among other things from a message format (e.g. HTML or formatted text), but mainly from a size and a number of additional files attached to e-mails (attachments). In case where the sender is located in a place near the recipient but his mail server is in a remote location, known methods generate a considerable load in network traffic. Let us consider the sender having an e-mail account handled by a server in Warsaw, Poland, who is on a business travel in Beijing, from where using mail user agent residing on his personal laptop computer he intends to send a message to a contractor being also in Beijing, whose server is installed in Chicago. The message shall be sent for the first time to the sender's server in Poland, then from Poland to Chicago and eventually back again to the recipient's in Beijing.
The aim of the invention is to provide a method and system of transferring electronic messages via telecommunication network, and particularly a method and system of transferring internet electronic messages (e-mails), which would cause a decrease in a network traffic load, wherein the implementation of the solutions according to the invention might be able to be gradually introduced to the existing environments of transferring messages (in other words the invention should feature backward compatibility in relation to existing systems). The aim of the invention is also providing a method and system of transferring electronic messages, which would provide considerably limitation of activity of entities responsible for spreading SPAM Messages.